A factor that might explain the increase in use was not mentioned in the article is the good efficacy of opioids against depression. A quick google search led to a short summary from last year. I have heard that from a few psychiatrist that found out that some people respond well to a low dose of Buprenorphine (Suboxone).

A quick look for depression map in the U.S. got me to this map from 2006/2008. The correlation is not perfect but I see some similarities to the one reported in the article. Would be interesting to see how an updated map looks like.